This invention relates to machine tools and more particularly to an improved system for holding down workpieces on the worktables of such machines.
In the woodworking, plastics, aerospace and other industries, CNC machines and particularly routers commonly have been used to machine workpieces of various materials including wood, plastic and nonferrous metals. Typically, such machines are provided with a worktable on which one or more workpieces are mounted to be machined or otherwise processed. In the past, such workpieces have been secured to the worktable mechanically by various means including bolts, clamps and the like. More recently, there have been developed systems utilizing vacuums for holding such workpieces in position, which have greatly improved productivity. Such systems have consisted of what have been termed conventional and universal systems. Conventional systems typically utilize a fixture equipped with a soft rubber seal that extends around the edge of the workpiece. Vacuum is applied to the zone within the seal which functions to hold the part to the fixture. Such type of system is commonly used to hold small workpieces. Universal vacuum systems typically have included a plenum provided in the worktable, connected to a vacuum pump and closed at its upper end by a porous spoilboard. In such systems, air drawn through the spoilboard by the vacuum applied to the plenum causes workpieces mounted on the spoilboard to be held fast to the spoilboard without the need of special fixtures or vacuum seals. Such continuous vacuum systems commonly have been used to hold relatively flat workpieces on worktables.
When used in their intended manner, the systems as described have been found to be highly effective in improving productivity. It has been found to be desirable, however, to provide a single holddown system which may be readily convertible to function either as a conventional or universal type of vacuum system.
The present invention provides a workpiece holddown system for the worktable of a machine tool generally consisting of means including a wall member for supporting one or more workpieces, defining a plenum connectable to a vacuum pump; means cooperable with a surface of a workpiece supported on the wall member, and an endless seal, defining a zone; means defining a passageway intercommunicating the plenum and the zone; and a valve disposed in such passageway. Such supporting wall member is particularly adapted to holddown comparatively small parts. When it is desired to process comparatively large, flat workpieces, such system may be converted into a universal type system merely by removing the supporting wall member and replacing it with a porous spoilboard.